As nation mourns, investigators try to figure out what led to tragedy in Newtown, Conn.

Federal investigators planned to visit dozens of shooting ranges and gun stores across Connecticut Sunday, attempting to figure out what led smart but painfully awkward 20-year-old Adam Lanza to murder 26 children and adults at Sandy Hook Elementary School in Newtown, while townspeople and President Obama attended an interfaith vigil amid sorrow and confusion.

The tragedy brought forth soul-searching and grief around the globe. Families as far away as Puerto Rico began to plan funerals for victims who still had their baby teeth, world leaders extended condolences, and vigils were held around the U.S.

Police said they had found "very good evidence" they hoped would answer questions about the motives of the gunman, described as brilliant but remote, who forced his way into the school in one of the world's worst mass shootings.

But Lt. Paul Vance of the Connecticut State Police said Sunday that there is no timeline for the motive to be revealed, and authorities still have an "immense" number of witnesses to interview. Vance warned that those posing as the gunman online or on social media -- and posting misinformation -- will be investigated and prosecuted for possible violations of Connecticut state and federal law.

On Friday morning, Lanza shot his mother, Nancy Lanza, four times in the head, authorities said.

He then drove to the school in her car with four guns, including a shotgun that was left in the back of the vehicle, and shot up two classrooms around 9:30 a.m., police say. Police added that multiple 30-round magazines and hundreds of bullets were also found at the scene.

The rifle used was a Bushmaster .223-caliber, according to an official with knowledge of the investigation who was not authorized to speak about it and talked on condition of anonymity. The gun is commonly seen at competitions and was the type used in the 2002 sniper killings in the Washington, D.C., area. Also found in the school were two handguns, a Glock 10 mm and a Sig Sauer 9 mm.

Sources told Fox News the guns used in the shooting were owned by and legally registered to Nancy Lanza.

Dean Price, director of the Wooster Mountain State Range -- a shooting range in Danbury -- said on Sunday that two ATF agents visited the range Friday night and stayed into the early morning looking through thousands of names on sign-in logs.

Lt. Vance said investigators are trying to trace the weapons back to the workbenches where they were assembled to try to figure out how and why they were used.

When Lanza arrived at the school, he forcibly entered, according to Connecticut Gov. Dannel Malloy.

"What we know is he shot his way into the building. He was not buzzed in," Malloy told ABC's "This Week" on Sunday. "He penetrated the building by literally shooting an entrance into the building."

A custodian ran through the halls, warning of a gunman on the loose, and someone switched on the intercom, alerting people in the building to the attack -- and perhaps saving many lives -- by letting them hear the hysteria going on in the school office, a teacher said. Teachers locked their doors and ordered children to huddle in a corner or hide in closets as shots echoed through the building.

Malloy said Lanza committed suicide when he heard first responders coming. A Connecticut official said Lanza killed himself with a single bullet to the head from the10 mm gun, and the bullet was recovered in a classroom wall.

"We surmise that it was during the second classroom episode that he heard responders coming and apparently at that, decided to take his own life," Malloy said.

Eighteen of the children and six more adults were dead at the school and two more children died later, Lt. Vance said Friday.

The gunman's father released a statement on Saturday.

"Our hearts go out to the families and friends who lost loved ones and to all those who were injured," Peter Lanza said. "Our family is grieving along with all those who have been affected by this enormous tragedy. No words can truly express how heartbroken we are. We are in a state of disbelief and trying to find whatever answers we can. We too are asking why. We have cooperated fully with law enforcement and will continue to do so. Like so many of you, we are saddened, but struggling to make sense of what has transpired."

The victims of the shooting were shot multiple times by a rifle, a medical examiner said Saturday, and Dr. H. Wayne Carver said the deaths are classified as homicides. Police began releasing the identities of the dead.

The well-liked principal, Dawn Hochsprung, was among them. A 27-year-old teacher, Victoria Soto, also reportedly hid some students in a bathroom or closet and died trying to shield them from bullets.

A funeral for one of the victims, 6-year-old Noah Pozner, is being planned for Monday. Pozner's uncle, Alexis Haller, says the funeral is scheduled for 1 p.m. at the Abraham L. Green & Son Funeral Home in Fairfield, Conn.

As the town mourned the deaths Sunday, a church service was temporarily evacuated after a caller "threatened to kill people in the church," a spokesman said.

Sunday evening, President Barack Obama attended an interfaith memorial service Sunday in Newtown -- the fourth time he has traveled to a city after a mass shooting.

The president had planned to travel to Maine Wednesday for an event promoting his positions in "fiscal cliff" negotiations, but the White House canceled that trip because of the shooting.

Obama was notified of the shooting about an hour after it occurred, White House officials said.

"Our hearts are broken today," Obama said in a brief address to the nation on Friday. "We've endured too many of these tragedies in these past few years, and each time I receive the news I react not as a president, but as a parent."

"Most victims were children, between five and 10 years old...They had their entire lives ahead of them, birthdays, graduations weddings, kids of their own," he said, pausing before wiping tears from his eyes.

The shooting came than two weeks before Christmas, was the nation's second-deadliest school shooting, exceeded only by the Virginia Tech massacre that claimed 33 lives in 2007.

On Friday, Lanza's brother, Ryan Lanza, 24, who was widely and erroneously reported to be the suspect, was questioned in Hoboken, N.J., but authorities said he was not involved. An FBI source tells Fox News that Ryan Lanza and the father, Peter Lanza, have both been cleared and are not longer being questioned.

Law enforcement officials have said they've found no note or manifesto from Lanza of the sort they have come to expect after murderous rampages such as the Virginia Tech bloodbath.

Vance said during Friday afternoon's news conference that police arrived at the scene "within minutes" of a 911 call placed shortly after 9:30 a.m. Friday.

"Every door, every crack, every crevice of that school" was checked, Vance said. “The entire school was searched.” He said the shooting occurred inside two rooms in "one section of the school."

Lanza was believed to suffer from a personality disorder and lived with his mother, said a law enforcement official who was briefed on the investigation but was not authorized to discuss it.

Education officials said they had found no link between Lanza's mother and the school, contrary to news reports that said she was a teacher there. Investigators said they believe Adam Lanza attended Sandy Hook Elementary many years ago, but they had no explanation for why he went there Friday.

Sandy Hook Elementary School has close to 700 students.

Newtown is in Fairfield County, about 45 miles southwest of Hartford and 60 miles northeast of New York City.